LESSONS IN ELECTRICITY 



171 



sealing-wax, A. Connect the sewing-needle with the machine, and 

 turn. A wind of a certain force is discharged from every point, and 

 the cross is urged round with the same force in the opposite direction. 

 You might easily, of course, so arrange the points that the wind 

 from some of them would neutralize the wind from others. But the 

 little pointed arms are to he so hent that the reaction in every case 

 shall not oppose, but add itself to, the others. 



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Fig. 21. 



The following experiments will yield you important information 

 regarding the action of points : Stand, as you have so often done be- 

 fore, upon a board supported by four warm tumblers. Hold a small 

 sewing-needle, with its point defended by the forefinger of your right 

 hand, toward your Dutch metal electroscope. Place your left hand 

 on the prime conductor of your machine. Let the handle be turned 

 by a friend or an assistant : the leaves of the electroscope open out a 

 little. Uncover the needle-point by the removal of your finger: the 

 leaves at once fly violently apart. 



Mount a stout wire upright on the conductor of your machine ; or 

 support the wire by sealing-wax, gutta-percha, or glass, at a distance 

 from the conductor. Connect both by a fine wire. Bend your stout 

 wire into a hook, and hang from it a tassel composed of many strips 

 of light paper. Work the machine. Electricity from the conductor 

 flows over the tassel, and the strips diverge. Hold your closed fist 

 toward the tassel, the strips of paper stretch toward it. Hold the 

 needle, defended by the finger, toward the tassel : atctration also en- 

 sues. Uncover the needle without moving the hand ; the strips re- 

 treat as if blown away by a wind. 



And now repeat Du Fay's experiment which led to the discovery 

 of two electricities. Excite your glass tube, and hold it in readiness, 

 while a friend, or an assistant, liberates a real gold or silver leaf in 



